Lake Untersee, November 2008. Dr. Valery Galchenko of the Winogradsky Institute of Microbiology, Russian Academy of Sciences, Russia is seen walking across the lake back to our camp.

Lake Untersee is one of the largest (11.4 km2) and deepest (&gt;160 m) freshwater lakes in East Antarctica. Located at 71•S, the lake has a perennial ice cover that varies in thickness along the main axis of the lake from 2.2 to 3.9 m. With the exception of a small anoxic basin in the southwest of the lake, the water column is generally well mixed, is supersaturated with dissolved oxygen, has a pH of 10.4 and exceedingly high clarity (vertical attenuation coefficient for PAR of 0.033 m-1). While the water column supports little primary production, the floor of the lake has an extensive cover of photosynthetic microbial mat to depths of at least 100 m. For more information, see: Andersen DT, Sumner DY, Hawes I, Webster-Brown J, McKay CP (2011) Discovery of large conical stromatolites in Lake Untersee, Antarctica. Geobiology, 9, 280-293. onlinelibrary.wiley.com/doi/10.1111/j.1472-4669.2011.00279.x/full We will be returning to Lake Untersee later this year. Our team members for the 2011 Tawani Antarctic Expedition are:

Our logistics support is being handled by ALCI: www.antarctic-company.com/alci.htm And we are working with the Arctic and Antarctic Research Institute in St. Petersburg, Russia: www.aari.aq/default_en.html Major funding for this project has been provided by the Robert A. Pritzker Center for Meteoritics and Polar Studies and the Trottier Family Foundation.

Additional support has been provided by the Russian Arctic and Antarctic Research Institute, St.Petersburg, Russia, the Von Braun Center, Huntsville, AL; NASA, and the Carl Sagan Center for the Study of Life in the Universe, SETI Institute, Mt. View, CA.

Gigapan Comments
(2)

The short answer is that the high pH is a result
of the weathering of the local rocks (anorthosite)
contributing hydroxyl (OH-) ions, along with the
presence of the ice-cover that helps keep CO2 from
dissolving in the water - which would reduce the
pH. The pH of the water is not so high that it
burns you - we drink the water and dive in it to
explore the lake bottom. Unfortunately the pH of
the lake water has been compared to bleach
elsewhere online, which is simply not true. The
longer answer, which can be found in our paper
about the lake (see the link above, you can
download the paper for free) is: The high pH has
been attributed to weathering of plagioclase
supplied by anorthosite in the lake catchment,
which produces high calcium, high pH, low
dissolved inorganic carbon (DIC) waters.
Specifically, plagioclase weathering consumes CO2
and, in water in equilibrium with the atmosphere,
raises pH to 8.3. Lake Untersee, however, appears
to be isolated from the atmosphere by the ice
cover, effectively limiting CO2 influx. Thus,
plagioclase weathering is dominated by reaction
with water, e.g.: 2NaCaAl3Si5O16 9 H2O = 2Na 2 Ca2
6OH- 4SiO2 3Al2Si2O5(OH)4, which in addition to
raising pH, provides abundant calcium (and silica)
to solution. Chemical modeling shows that this
situation is stable only when DIC is maintained at
low concentration (30 μmol/l); any influx of CO2
results in precipitation of calcite and a drop in
pH (Andersen et al. 2011).